The present invention relates to an improved process and system for high strength organic waste water treatment. Specifically, the invention relates to a novel process and system for processing the high strength waste water streams issuing from a variety of primary facilities including food processing plants (e.g. potato, rice, grain processing), brewery plants, dairy processing, pharmaceutical plants, or the like in order to insure that the effluent discharge into municipal sewage systems and water ways is environmentally safe and free from harmful biological contaminants. The novel process and system of the present invention provides the additional function of producing a valuable single cell protein product having direct commercial use as animal feed and as a protein and flavoring supplement in human foodstuffs.
In most food, beer, dairy, or pharmaceutical processing facilities, there are waste water by-products that consist of water, soluble organics, and solid wastes. The waste water often includes an unacceptable level of biological waste products measured in terms of its Biological Oxygen Demand ("BOD"). Generally, the BOD level in an organic waste stream is directly related to the carbon content in the waste stream wherein the carbon is typically in the form of starch (C.sub.6 H.sub.10 O.sub.5).sub.n. or sugar C.sub.6 H.sub.12 O.sub.6. When an organic stream is injected into the environment, generally, and into a water body or ground water, specifically, aerobic bacteria use oxygen to degrade the complex organic compounds in the waste stream to simpler and environmentally neutral species such as CO.sub.2, NO.sub.3.sup.- ions, and SO.sub.4.sup.-2 ions. The organic compounds undergo a decomposition process driven by the available oxygen supply and that reduces the amount of dissolved oxygen in the water. When the carbon content of a waste stream is high (i.e. a high BOD level), anaerobic bacteria take over the decomposition process, forming rather noxious environmentally harmful pollutants including methane CH.sub.4, ammonia NH.sub.3, and hydrogen sulfide H.sub.2 S. Moreover, animal life can not survive in this environment because of the depletion of the oxygen supply in the water.
The BOD level of a water stream is determined by measuring the amount of oxygen consumed by a sample of known volume. The concentration of dissolved oxygen in the diluted sample is determined immediately and again after a period of five days. From the decreased oxygen concentration, a calculation of the BOD level in the water stream is made: ##EQU1##
Generally, a BOD of 0 to 10 is characteristic of pure water. BOD values higher than 10, however, indicate water of doubtful purity. For example, untreated municipal sewage can have a BOD of 100 to 400 and some industrial wastes can have BOD values in the order of 10,000.
In the last decade, environmental concerns have altered the way waste water streams are dealt with in the industry. Of course, many Federal, State, and local regulations place strict controls on the nature of waste streams issued into the environment. Most municipalities require that an effluent contain less than 30 parts per million (ppm) organic species. Many solutions to the environmental concerns discussed above have been proposed.
One such proposal is directed to treating the volatile organic waste in the form of manure from the feedlot of cattle or other farm animals. As disclosed in U.S. Pat. No. 4,041,182 to Erickson et al., the first step comprises grinding or shredding the input materials to a course particulate size and subjecting the input materials to a biological decomposition using a broad spectrum enzyme complex capable of hydrolyzing the insoluble high molecular weight proteins and starches. Another step involves mechanical separation and dewatering of the non-volatile solids fraction of the raw materials (consisting mainly of cellulose and lignin). Erickson et al. discloses that the resulting material is subjected to an inoculating solution of synthesizing microorganisms. These microorganisms consist of single cell bacteria which undergo exponential growth. The Erickson et al. process essentially serves as a deodorizing plant that permits a portion of the by-product to be recycled back to the farm land.
The Erickson et al. use of a bacteria converting agent is problematic. First, many different bacteria strains are created in an unpredictable and uncontrolled process. Some of these bacteria strains can be very harmful and even deadly to humans, e.g. e-coli, and the different bacteria strains can cross-contaminate one another. As such, the biological by-product of the Erickson et al. process is not useful as a human food supplement nor as a livestock feed. Moreover, bacteria as an animal feed is less valuable than alterative additives such as yeast. Because bacteria is still in a complex protein form, it requires digestion by the animal as opposed to being a direct source of amino acids and growth nutrients. Bacteria is a low grade product unacceptable in most applications.
Similarly, U.S. Pat. No. 4,018,650 to Busta et al. discloses a waste treatment process using two different bacteria strains: Bacillus and Lactobacillus. The Busta et al. process is limited to streams containing both a protein source and a carbohydrate source. Moreover, the disclosed process utilizes a batch system which is not practical in most commercial applications. Burdensome set up procedures are required by forming a specified waste batch with a specified ratio of collagen and starch, again not practical in most commercial applications.
U.S. Pat. No. 4,617,123 to Christ offers an alternative treatment solution for a waste stream. Christ presents a process for treating the waste waters issuing from the manufacture of sauerkraut. Christ subjects the entire stream of waste water to a biological process utilizing an inoculum consisting of Candid crusei and Candid utilis. After the biological treatment, Christ treats the stream to a reverse osmosis in order to form a purified liquid effluent having a purity higher than 99%. Christ makes no provisions for controlling the yeast fermentation process including identifying pH levels and necessary control additives. The Christ process is further disadvantageous because it requires subjecting the entire waste stream to the biological process--a cost prohibitive feature in larger food processing plants. Although Christ discloses a preferred yeast type in the processing of sauerkraut waste, he makes no provisions for yeast selection in other classes of waste streams.
The difficulties and limitations suggested in the preceding are not intended to be exhaustive, but rather are among many which demonstrate that although significant attention has been devoted to waste treatment processes and systems, such methods and systems appearing in the past will admit to worthwhile improvement.